This disclosure is related to the field of subsurface wellbore drilling unit automation. More specifically, the disclosure relates to systems for synchronizing a plurality of independently operating automatic drilling task apparatus used on a drilling unit to enable the possibility of full automation and optimization of drilling unit operations.
Drilling unit (drilling “rig”) components include devices used to movably support a drill bit mounted on the end of a conduit called a “drill string.” The drill string is typically formed from lengths of drill pipe or similar tubular segments connected end to end. The drill string is supported by the drilling rig structure at the Earth's surface when a wellbore is drilled on land, or when drilled below the bottom of a body of water from a water bottom supported platform or a floating structure. The drill string may be rotated by equipment on the drilling rig, e.g., a swivel/kelly/rotary table combination or a top drive, to rotate the drill bit. In some instances, a motor such as a fluid operated motor may be included in the drill string and may also be used to rotate the drill bit.
A drilling fluid made up of a base fluid, typically water or oil, and various additives, is pumped down a central opening in the drill string. The drilling fluid exits the drill string through openings called “jets” in the body of the drill bit. The drilling fluid then circulates back up an annular space formed between the wellbore wall and the drill string, carrying the cuttings from the drill bit so as to clean the wellbore. The drilling fluid may also be formulated such that the pressure exerted in the wellbore by the drilling fluid is at least as much as surrounding formation fluid pressure, thereby preventing formation fluids from entering into the wellbore.
The drilling fluid pressure typically exceeds the formation fluid pressure by some amount, which results in drilling fluid entering into the formation pores, or “invading” the formations exposed by drilling the wellbore. To reduce the amount of drilling fluid lost through such invasion, some of the additives in the drilling fluid adhere to the wellbore wall along permeable formations thus forming a relatively impermeable “mud cake” on the wellbore wall adjacent to such formations. Mud cake substantially stops continued invasion, which helps to preserve and protect the exposed formations prior to the setting of protective pipe or casing in the wellbore as part of the well construction process, as will be discussed further below. The formulation of the drilling fluid to exert hydrostatic pressure in excess of formation pressure is commonly referred to as “overbalanced drilling.”
The drilling fluid ultimately returns to the surface, where it is transferred into a mud treating system, generally including components such as a shaker table to remove solids from the drilling fluid, a degasser to remove dissolved gases from the drilling fluid, a storage tank or “mud pit” and a manual or automatic means for addition of various chemicals or additives to the fluid treated by the foregoing components. The clean, treated drilling fluid flow is typically measured to determine fluid losses to exposed formations as a result of the previously described fluid invasion. The returned solids and fluid (prior to treatment) may be evaluated to determine various Earth formation characteristics used in drilling operations. Once the drilling fluid has been treated in the mud pit, it is then pumped out of the mud pit and is pumped into the drill string again.
One may conceptualize automation of processes implemented by drilling rig apparatus such as those described above using a three-layer architecture: deliberative control; reactive plan execution and feedback control. Deliberative control, the top layer, is slow and requires abstraction of control concepts. Deliberative control is where well construction planning decisions are made, e.g., and without limitation, an initial well plan including diameter of drill bits used and depths to which sections of the wellbore are to be drilled, well geodetic trajectory, casing depths, drilling fluid properties and drilling fluid flow rates. Reactive plan execution, the middle layer, translates the abstract plan generated in the deliberative control layer into machine operating instructions (whether automatically performed or manually performed by a drilling unit operator) to the feedback control layer. Reactive plan execution includes communication to the deliberative control layer of the degree to which the wellbore as actually constructed conforms to a predetermined construction plan or failure thereof, i.e., the inability of the drilling rig components to execute the predetermined construction plan.
Drilling rig operations may be referred to as “multi-tenants.” A simplified view of a drilling rig system conceptualized as “multi-tenant” may include the well “operator” (e.g., an oil and gas exploration and production entity) which defines high-level goals (e.g., the predetermined well construction plan) and therefore mostly operates in the deliberative control layer. Based on a set of constraints and goals, the well operator produces the highest level of planning. A drilling contractor, i.e., the owner/operator of the drilling rig may receive well plans from the operator and execute them. The drilling contractor may monitor the operation of the drilling rig so as to execute the predetermined well construction plan, and may attempt to recover from any execution failure. Certain tasks may be outsourced to specific service companies for highly specialized control actions, e.g., and without limitation, drilling fluid composition control, acquisition of formation petrophysical measurements and selection and control of wellbore annulus pressure. Equipment manufacturers operate mostly in the feedback control layer: they design the equipment and design (or OEM) the control systems for such equipment
One of the issues that requires addressing in automating control of drilling rig equipment as described above is high fragmentation of control systems and the large number of entities responsible for reactive plan execution. Separate control systems operate fluid pumping, drill string rotation and drill string hoisting systems, for example. A number of advanced control algorithms require high fidelity control of two or more of such control systems, and the same high fidelity in correlating control system operating signals with sensor measurements. Existing closed-loop control systems already provide high-fidelity actuation of specific subsystems to a high degree of precision, but do not address time synchronization, i.e., start time of a particular control sequence at a predetermined moment in time.
Multi-controller advanced control algorithms require strongly coupled behavior of disparate, independently-designed and developed control subsystems in order to effectively automate operation of the various systems on a drilling rig.